Many different processes for joining together printed paper sheets to form an end product are known. In the printing field particular use is made of wire stitching processes, in which folded paper sheets are joined together in the fold by means of staples. Occasionally in a preliminary stage a stitching of partial products take place and in a subsequent process stage they are inserted in an end product and connected thereto.
A two-stage process has proved satisfactory for the binding of top quality books. In a first process stage the printed sheets are combined with one another by thread binding to form a booklet, leaflet or the like and in a second stage several booklets or leaflets are combined in an adhesive binding process. In these binding processes the individual booklets must be juxtaposed, so that the book back is freely accessible for mull lining and back adhesive coating. This process is unsuitable for the production of newspapers and periodicals.
Two-stage binding is also used in the production of printed products in high capacity printing plants. The reasons for a two- or multiple-stage binding are inter alia that partial products are often produced in different partial processes, e.g. on different printing plants or in time-displaced production phases. The partial processes can e.g. be integrated in to a rotary printing process. Unlike in the aforementioned book binding method, in said process the individual booklets are not juxtaposed and are instead inserted in one another. Innovations in the mechanical binding of paper layers became necessary when high capacity printing plants became available, which were able to produce up to 100,000 printed products every hour.
Thus, besides other conventional binding possibilities of late the possibility of adhesive binding has become known, in which the adhesive is injected into the fold of the printed product. The corresponding injection adhesion process is described in Swiss Patent Application 1155/89-3 (corresponding to EP 0390734), whose content is assumed as known for the present application.
However, great significance is still attached to wire stitching. The latter inter alia provides the possibility of integrating the stitching process into the printing process as a result of rotary wire stitchers. Such stitching systems have a high capacity, but are relatively expensive. A booklet or leaflet can have up to about 100 pages. The paper is folded after stitching. In the case of rotary wire stitching the staples are pressed through the spread-out paper piles against an abutment without a locking mechanism. Therefore the stitching is not of high quality. The wire ends can easily project from the paper, which can be disadvantageous during the further processing.
In other applications use can be made of so-called single wire stitching, but this has a lower capacity, i.e. less printed products can be processed per unit of time than in the case of rotary wire stitching. However, the product can have over 300 pages. Single or individual wire stitchers have a stitching abutment with a locking mechanism, but such systems are expensive.
An advantage of wire stitching is that the finished product can be completely opened. There is no closed folding edge covering part of the printed information. However, wire stitching also suffers from significant disadvantages. Apart from the problem of material application through the staples in the back, there are limits to the reliability of wire stitching if it is necessary to produce thick end products with 200 or more pages.
However, conventional adhesive binding, which would fundamentally be suitable for large products and in which the paper layers are bundled, milled and subsequently back-bonded, cannot be used in connection with high capacity printing plants. The reason for this is in particular the long drying time and the associated relatively slow processing rate.
There is nowadays an increasing need, particularly in the production of large end products using high speed processes to gather together prefabricated partial products in an appropriate manner and then bind the same. However, the known processes only offer unsatisfactory possibilities in this connection or are unable to fulfil the requirements as regards quality, speed, flexibility and cost.
However, it is far from simple to solve this problem. The subsequent joining together of already stitched partial products is also problematical in other respects. When joining together stapled booklets with an additional staple there is e.g. a risk of the second staple being impeded by the initial staple on pressing in, so that a reliable connection is not obtained. This problem can admittedly be counteracted by assuring that the two staples are displaced on the back. However, when simultaneously using the same wire stitching device for both binding processes this makes it necessary for adjustments between the processing steps, which leads to technical problems and involves corresponding additional costs. The adjustment is particularly difficult in the case of single wire stitchers having a stitching abutment with a locking mechanism. In generalizing, the problem is that the process used for joining together the partial products and the subsequent process of gathering and joining said partial products to the end product must not impede one another. In addition, the combination of wire stitching with conventional adhesive stitching is problematical, because the pressing of the staples through the glued back can be hindered.
It must finally also be borne in mind that a process for joining partial products must be easily integratable in to conventional further processing operations and must not lead to additional problems in the gathering of the partial products, particularly in high speed processes, i.e. where about 100,000 copies have to be produced every hour.